This invention relates to electromechanical systems and techniques for fabricating microelectromechanical and/or nanoelectromechanical systems; and more particularly, in one aspect, to fabricating or manufacturing microelectromechanical and nanoelectromechanical systems having mechanical structures that are encapsulated using thin film or wafer bonding encapsulation techniques, and including suitable anti-stiction characteristics.
Microelectromechanical systems (“MEMS”), for example, gyroscopes, resonators and accelerometers, utilize micromachining techniques (i.e., lithographic and other precision fabrication techniques) to reduce mechanical components to a scale that is generally comparable to microelectronics. MEMS typically include a mechanical structure fabricated from or on, for example, a silicon substrate using micromachining techniques.
MEMS often operate through the movement of certain elements or electrodes, relative to fixed or stationary electrodes, of the mechanical structures. This movement tends to result in a change in gap distances between moving electrodes and stationary or fixed electrodes (for example, the gap between opposing electrodes). (See, for example, U.S. Pat. Nos. 6,240,782, 6,450,029, 6,500,348, 6,577,040, 6,624,726, and U.S. Patent Applications 2003/0089394, 2003/0160539, and 2003/0173864). For example, the MEMS may be based on the position of a deflectable or movable electrode of a mechanical structure relative to a stationary electrode.
The mechanical structures are typically sealed in a chamber. The delicate mechanical structure may be sealed in, for example, a hermetically sealed metal container (for example, a TO-8 “can”, see, for example, U.S. Pat. No. 6,307,815), bonded to a semiconductor or glass-like substrate having a chamber to house, accommodate or cover the mechanical structure (see, for example, U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and 6,507,082), or encapsulated by a thin film using micromachining techniques during, for example, wafer level packaging of the mechanical structures. (See, for example, International Published Patent Applications Nos. WO 01/77008 A1 and WO 01/77009 A1).
In the context of the hermetically sealed metal container, the substrate on, or in which the mechanical structure resides may be disposed in and affixed to the metal container. The hermetically sealed metal container also serves as a primary package as well.
In the context of the semiconductor or glass-like substrate packaging technique, the substrate of the mechanical structure may be bonded to another substrate whereby the bonded substrates form a chamber within which the mechanical structure resides. In this way, the operating environment of the mechanical structure may be controlled and the structure itself protected from, for example, inadvertent contact. The two bonded substrates may or may not be the primary package for the MEMS as well.
Thin film wafer level packaging employs micromachining techniques to encapsulate the mechanical structure in a chamber using, for example, a conventional oxide (SiO.sub.2) deposited or formed using conventional techniques (i.e., oxidation using low temperature techniques (LTO), tetraethoxysilane (TEOS) or the like). (See, for example, WO 01/77008 A1, FIGS. 2-4). When implementing this technique, the mechanical structure is encapsulated prior to packaging and/or integration with integrated circuitry.
Under certain conditions, for example, during operation, the deflectable or movable electrode may contact the stationary or fixed electrode and the electrodes may become stuck. This may be the result of, for example, rapid, sudden and/or violent acceleration of the MEMS. When electrodes of a mechanical structure become stuck, it is generally known as stiction. Stiction is common in MEMS and may be caused by, for example, van der Waals force, cold welding, arcing, molecular or atomic bonding, surface tension of, for example, liquids formed on the contacting parts, and/or electrostatic forces due to surface charge. Stiction typically renders the MEMS inoperative.
There are many different and diverse techniques/approaches to address, minimize, overcome and/or avoid the debilitating affects of stiction. (See, for example, U.S. Pat. Nos. 6,621,392, 6,625,047 and 6,625,342 and U.S. Patent Application Nos. 2003/0155643 and 2003/0178635). One approach is to apply a lubricant or passivation layer, for example, perfluorodecanoic acid (“PFDA”) on the mechanical structure, including the movable and fixed electrodes. In this regard, PFDA may be deposited in a monolayer, typically through a vapor deposition, and forms an extremely low energy surface. (See, for example, U.S. Patent Application No. 2003/0161949). This approach is quite common in substrate packaging technique.
In wafer level packaging of mechanical structures, however, the thin encapsulation film is often deposited at high temperatures. In addition, additional or further processing, for example, MEMS integration with electronic circuitry often requires use of high temperature processes (for example, during the formation or fabrication of the integrated circuits). Conventional lubricants or passivation layers are susceptible to destruction when subjected to those temperatures required for fabricating the thin film encapsulation or integrated circuits. Thus, after encapsulation, the mechanical structures are more prone to stiction as a consequence of the post-mechanical structure processing.
There is a need for, among other things, a MEMS employing an anti-stiction technique that is compatible with thin film encapsulation and/or wafer bonding techniques and overcomes one, some or all of the shortcomings of the conventional anti-stiction techniques. There is a need for, among other things, a MEMS having mechanical structure that is encapsulated using thin film encapsulation and/or wafer bonding techniques, that possesses suitable anti-stiction techniques and overcomes the cost, design, operation and/or manufacturing shortcomings of conventional anti-stiction techniques. There is a need for a MEMS having low adhesion energy mechanical structures that are encapsulated using wafer level thin film and/or wafer bonding encapsulation techniques.